You need to tell photoslop what "scratch disks" you want to use. "Best Policy" is to have two drives, or two partitions, with your OS on one and your proggies on another. That way you can tell PS to use the D: drive for it's scratch disk.
In Photoshop go to: "Edit/Preferences/Plug in's and Scratch disks" and you can set the correct drive there.
Wedo